JP2019513574A - Flexible packaging substrate comprising thermally stable printed matter - Google Patents

Abstract

The present invention relates to a flexible packaging substrate comprising one or more cross-linked ink layers, and to a method for producing said printed substrate.
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Description

  The present invention relates to a printed packaging substrate and a method of manufacturing a flexible packaging substrate comprising a thermally stable digital print.

  In the flexible packaging industry, it has been an ongoing trend for many years to reduce the time it takes to market from the owner of the brand to the end consumer. The customization of packaging and the enthusiastic promotional campaigns directed to the consumer require the ability of the processor to respond quickly, efficiently and flexibly (flexibly) with the ready printing campaign. Also, at the package design stage, the production of a full-size model sample with a printed sample for the final product requires rapid and flexible (flexible) printing techniques.

  The term "flexible packaging" is intended to mean a thin film or foil material, generally supplied in roll form, printed and rewound after printing. Exemplary flexible packaging substrates include common plastic and polymer films, metallized polymer films, metal foils, laminates thereof, and laminates of polymer films and paper or polymer coated paper, and the like. Flexible packaging substrates can be used, for example, for packaging food, pharmaceuticals, cosmetics, tobacco and the like.

  Packaging printing and decoration techniques are dominated by liquid-ink processes, which are based on drying or curing individual ink layers through evaporation of water or volatile organic compounds. These processes consume a great deal of energy and often adversely affect the environment by releasing solvents or greenhouse gases into the atmosphere.

  The introduction of radiation curable inks, such as ultraviolet (UV) and electron beam (EB) curable inks, helps to reduce this type of emission.

  Two major techniques are used in radiation curable inks. The first technique uses free radical species to initiate the polymerization of reactive functional groups, in particular ethylenically unsaturated double bonds. The most commonly used reactive groups are (meth) acrylates, in particular acrylate groups, for example those as described in WO 97/31071, US2015 / 0116432 and US2015 / 0184005.

  One limitation of radiation curable (meth) acrylate based inks is the flexibility of the cured ink. This is generally associated with the shrinkage associated with the acrylate material after curing, making the ink film brittle and not suitable for applications where high flexibility is required.

  Another technique used in radiation curing is to generate very strong acids to cationically react reactive functional groups such as cyclic ethers such as oxiranes and oxetanes, preferably cycloaliphatic epoxides, allyl ethers, and vinyl ethers. It is to start polymerization. This technique is described, for example, in US Pat. No. 5,674,922 and US 2010/0136300.

  The advantages of cationic curing over radiation curing include low shrinkage and thus good adhesion and excellent flexibility. In addition, cationic systems are not sensitive to oxygen inhibition, thus allowing substantially complete (ie 100% or about 100%) monomer conversion. This means that cationic techniques can cure thick pigmented ink films much more easily than free radical techniques.

  The use of radiation curable inks for use in flexible packaging is extensively described in the literature.

  US 2008/0218570 A1 discloses a method and apparatus for forming high quality and high throughput ultraviolet or electron beam curable gel ink images on flexible substrates for packaging applications.

  EP 21 33 210 A1 and EP 27 208 77 A1 are packaging materials (e.g. paper, cardboard and various flexible polymer films) by exposing multiple layers of curable ink and coating that do not substantially change viscosity during the printing process to electron beams. Discloses a method of printing and decorating. The ink and coating are essentially free of volatile components prior to, during, and after electron beam irradiation. The method comprises applying an ink and optionally multiple layers of a coating on a substrate. The layers are then simultaneously exposed to electron beam radiation, which results in the polymerization or crosslinking of the ethylenically unsaturated component and drying.

  EP 074 1 644 A1 discloses a system and method for printing of a substrate for use in food packaging. Specifically, this EP publication describes a flexographic printing system for applying and curing a radiation curable ink on a flexible (flexible) heat shrinkable web using a combination of UV radiation and EB radiation Disclose the method.

  EP 2305758 A1 relates to a laminate comprising a) a substrate comprising a thermoplastic polymer and b) a single layer or multilayer ink film and / or a varnish film comprising a printing ink or a printing varnish. The printing ink or printing varnish comprises a binder having a non-radiation curable aromatic polycarbonate and a solvent comprising at least one radiation curable monomer, which comprises an acrylate, a methacrylate, a vinyl ether, and an ethylenic double bond. Are selected from the group consisting of nitrogen containing compounds having The binder is dissolved in a solvent, which is bound in chemically crosslinked form in the printing ink or printing varnish after curing.

  US 2002/119295 A1 discloses an article comprising a first and a second outer surface. The article has an image printed on the first outer surface and a radiation curable varnish applied on the first outer surface to cover at least a portion of the image.

  EP 1159142 A1 discloses a printed packaging material in which the printed image is arranged on the main surface. This image contains two major components. The first component is at least one marking comprising a pigment. The second component is a pigment free coating which covers the outermost marking. The coating is formed of a material that can polymerize and / or crosslink when exposed to ionizing radiation. After the film is exposed to such radiation, the coating cures to form a protective layer covering the printed markings.

  US 2013/0233189 A1 discloses a flexible substrate in which a radiation curable ink is applied to the substrate and an overcoat layer is applied to the cured ink.

  Cationic curable inks are reported, for example, in JP 10-324836, U.S. Pat. No. 5,889,084 and U.S. 2005/187309 A1.

  Among the disadvantages of radiation curable inks, the complexity of the printing process, and the formation of low molecular weight compounds, can be mentioned as endangering their use for food and pharmaceutical packaging.

  New technologies have emerged over the past few decades, with more or less success, in addition to the conventional printing techniques applied in flexible packaging (eg, gravure and flexographic printing). The key critical parameters for investment and for the decisive success of the technology in certain markets are: investment costs, machine speed, achievable web width, preparation time before pressing, preferred color Availability, flexibility of design changes, print quality, promotion of ink adhesion to the substrate, product safety aspects of the ink, stability of the ink to temperature and UV light.

  Among these new technologies, digital printing (e.g., inkjet printing and liquid electrophotography) is of most interest.

  Digital printing apparatus and methods are known in the printing art and are generally described, for example, in US6608986; US6529288; US6539858; US6162570; US5819667 and US5777576.

  A technology that has gained wide attention in flexible packaging is digital offset technology or liquid electrophotography. Digital printing is inherently flexible and quick in design change. The reason is that the physical printing plate is not applied. The image remains purely digital.

  Generally, digital offset techniques cause the laser to form an image on the photoconductive surface, apply the ink with charged particles to the photoconductive surface, selectively couple them to the image, and Transferring the charged particles of the form to the printing substrate.

  The photoconductive surface is usually on a cylinder and is often referred to as the "photoimaging plate (PIP)". The photoconductive surface is selectively charged at the latent electrostatic image with the image and the background area with different potentials. For example, an electrostatic ink composition comprising charged particles in a carrier liquid can be contacted with a selectively charged photoconductive surface. The charged particles adhere to the image area of the latent image. On the other hand, the background area remains unattached. The image is then transferred directly to the printing substrate, or more commonly first transferred to an intermediate transfer member, which can be a soft swellable blanket, and then the printing substrate It is transferred to the material. Ink transfer is forced by the applied electric field and the carrier ink liquid evaporates from the blanket. Hot melt inks are adhered to substrates by pressure and tack. This process is repeated for each color. Primarily, the ink transfers to the substrate without change and without penetrating the substrate. Thus, the quality of the image obtained is very high and appears to be independent of the properties of the substrate.

  Variations of this method utilize various methods to form an electrostatic latent image on the photoreceptor or on the dielectric material.

  Electrophotographic printing on plastic, paper, or metal is disclosed, for example, in US201102562578.

  Inks, especially those developed for liquid electrophotography, are designed to form high resolution, uniform gloss, sharp image edges, and thin image layers, and are generally carrier liquids, resins, and pigments. Containing agents. Typical carrier liquids can include mixtures of various agents such as surfactants, dispersants, cosolvents, viscosity modifiers, and / or other possible components.

  The main limitation of flexible substrates printed by liquid electrophotography is the thermal stability of traditional ink based prints. In particular, in direct contact sealing applications, the printed matter on the surface of the substrate is damaged by the limited thermal stability of the ink, in direct contact with the sealing jaws of the flexible packaging machine. Depending on the packaging speed and the application, the typical temperature range on film sealing machines in vertical and horizontal form is 120-200 <0> C. The lack of heat resistance of the ink after sealing results in the softening of the ink under the pressure of the sealing jaw and the change of color and deformation of the design due to the flow of the ink.

  A typical solution to overcome this problem is to apply a surface protection coating as disclosed, for example, in EP 1159142 A1; US 2005/019533 A1; US 2007/085983 A1;

  Limitations to this approach are the lack of intercoat adhesion between the coating and the ink, and the high gloss, high optical quality, and risk of appearance change of the ink after application of the coating. Furthermore, in the particular case of a solvent or water based protective coating, removal of the solvent and / or water is necessary in the heat sensitive operation step.

  The present invention provides a flexible package comprising digital printed matter and a method for producing a printed flexible package, wherein the printed flexible package exhibits particular advantages compared to the prior art mentioned above. The purpose is

  The present invention is a flexible packaging substrate comprising one or more crosslinked ink layers, wherein the concentration of ethylenically unsaturated groups and cycloaliphatic epoxides in said ink layers is preferably less than 0.05 meq / g, preferably Discloses a flexible packaging substrate which is less than 0.03 meq / g, more preferably less than 0.01 meq / g, most preferably less than 0.005 meq / g.

Preferred embodiments of the invention disclose one or more of the following features.
The flexible packaging substrate does not contain an additional layer protecting the one or more crosslinked ink layers.
The flexible packaging substrate comprises a primer layer sandwiched between the crosslinked ink layer and the substrate.
The total layer thickness of the primer layer and the ink layer is 0.4 to 4 μm, preferably 0.6 to 3.5 μm, more preferably 0.8 to 3 μm.
The layer thickness of the primer layer is from 0.01 to 0.5 μm, preferably from 0.05 to 0.4 μm, most preferably from 0.1 to 0.3 μm.

The present invention is a method of forming a printed flexible packaging substrate, comprising:
a) preparing a flexible packaging substrate;
b) applying at least one digital print by digital printing process of at least one ink composition, wherein said ink composition substantially comprises (meth) acrylic double bond and / or cycloaliphatic epoxide C) subjecting the digital print to electron beam irradiation;
Further disclosed is a method characterized in that the method comprises:

Preferred embodiments of the method of forming a printed flexible substrate disclose one or more of the following features.
-At least one ink composition is substantially free of components comprising molecular structures having pendent and / or terminal ethylenic unsaturated double bonds.
-The flexible packaging substrate is plasma treated, preferably corona plasma treated.
The method comprises the additional step of applying the primer composition before the start of step b).
The digital printing process of step b) is liquid electrophotographic printing.
The dose of electron beam irradiation in step c) is at least 15 kGy, preferably at least 18 kGy, more preferably at least 20 kGy.
The dose of electron beam irradiation in step c) is 20-100 kGy, preferably 25-80 kGy, more preferably 30-60 kGy.
-Electron beam irradiation in step c) is performed with an oxygen concentration of less than 300 ppm, preferably less than 250 ppm, more preferably less than 200 ppm, most preferably less than 150 ppm.
The flexible packaging substrate of step a) comprises polyethylene terephthalate, high density polyethylene, oriented polypropylene, oriented polyamide, polystyrene or paper.
The primer composition comprises one or more polyacrylamides.
The ink composition comprises one or more (meth) acrylic (co) polymer resins.
The ink composition comprises 20 to 95% by weight of a hydrocarbon carrier liquid, 5 to 80% by weight of one or more (meth) acrylic (co) polymer resins, and 10 to 50% by weight of one or more carboxyl functionalities The ethylene-containing copolymer co-resin and 0.1 to 80% by weight of one or more colorants.
The method comprises the additional step of laminating the flexible packaging substrate to the sealing layer.
The method comprises heat sealing the printed flexible packaging substrate or laminate in a heat sealing apparatus at a temperature of 100 to 250 ° C., preferably 110 to 230 ° C., more preferably 120 to 220 ° C. .

  The invention further discloses a flow pack characterized in that it comprises a flexible packaging substrate.

  The present invention discloses a flexible packaging substrate comprising a thermally stable digital print, preferably a thermally stable digital print obtained from liquid electrophotographic printing. The thermal stability is obtained by subjecting the printed matter to electron beam irradiation.

  Thermal stability of digital prints is a prerequisite for heat sealing, especially in direct contact applications where the ink comes in direct contact with the sealing jaws of the packaging machine at the surface of the substrate. The lack of heat resistance of the print after sealing results in the softening of the ink under the influence of the sealing jaws and the change of color and deformation of the design due to the flow of ink.

  We use the ink formulation even if it is a digital print, preferably a digital print obtained from liquid electrophotographic printing of a conventional ink formulation that is not perceived as a UV or electron beam curable ink. It has surprisingly been found that it is thermally stable through electron beam radiation if it comprises an acrylic copolymer resin and is substantially free of (meth) acrylic double bonds and / or cycloaliphatic epoxides.

  Flexible packaging substrates comprising electron beam-irradiated digital prints enable heat sealing without the need to place an additional protective layer on top of the prints.

  The components making up the ink for use in the present invention are dangling or end-standing ethylenically unsaturated functional groups (eg, (meth) acrylic, vinyl, allyl, and It does not substantially contain the functional group of fumaric acid ester.

  In the context of the present invention, "hanging ethylenically unsaturated group" means a functional group which is not incorporated in the molecular skeleton, which is, for example, in unsaturated polyesters and in butanediene-containing (co) polymers. be able to.

  In the present invention, “substantially free of ethylenically unsaturated group” means that the concentration of the ethylenically unsaturated group is less than 0.2 meq / g, preferably less than 0.1 meq / g, more preferably 0.05 meq / g. It means less than g, most preferably less than 0.01 meq / g.

  In the present invention, the "substantially free of alicyclic epoxide" means that the concentration of alicyclic epoxide is less than 0.2 meq / g, preferably less than 0.1 meq / g, more preferably less than 0.05 meq / g , Most preferably less than 0.01 meq / g.

  Preferably, the ink formulation for use in the present invention does not contain (meth) acrylic double bonds and / or cycloaliphatic epoxides.

  Preferably, the ink formulation for use in the present invention does not include pendent or terminal ethylenic unsaturated functional groups (eg, vinyl, allyl and fumaric acid ester functional groups).

  Prior art resins specifically developed for UV and electron beam curing generally have concentrations of ethylenically unsaturated groups or cycloaliphatic epoxides higher than 1.0 meq / g and even higher than 1.5 meq / g It is characterized by This high concentration is sought for reactivity reasons.

  Despite the substantial absence of such ethylenically unsaturated groups or cycloaliphatic epoxides, in the inks used in the present invention, electron beam radiation crosslinks the polymer chains. The crosslinks are preferably carbon-carbon crosslinks.

  Preferably, the carbon-carbon bridge of the electron beam crosslinked ink of the present invention is characterized in that the carbon atom is a tertiary or quaternary carbon atom.

More preferably, the carbon-carbon bridge is of the (R ¹ ) ₂ R ² C—C (R ¹ ) ₂ R ₃ type, where R ¹ is a (meth) acrylic copolymer segment, R ² Is a hydrogen atom or a (meth) acrylic copolymer segment, R ³ is a hydrogen atom, a methyl group, or a (meth) acrylic copolymer segment, which are as determined by Fourier transform infrared spectroscopy.

  Crosslinked ink obtained from irradiation of an ink designed for crosslinking under the influence of UV or EB, wherein the residual ethylenicity in the ink comprises a significant concentration of ethylenically unsaturated groups or cycloaliphatic epoxides The concentration of unsaturated group or cycloaliphatic epoxide is higher than 0.05 meq / g, more preferably higher than 0.1 meq / g, most preferably higher than 0.2 meq / g.

  Cross-linked conventional UV and EB inks are characterized by the inclusion of residual ethylenically unsaturated groups and / or cycloaliphatic epoxides resulting from insufficient conversion due to the increase in viscosity as the degree of crosslinking is increased.

  The concentration of the ethylenically unsaturated group or cycloaliphatic epoxide, and the degree of conversion can be determined by titration of the combination, for example, by iodate titration and Fourier transform infrared spectroscopy.

  The concentration of the ethylenically unsaturated group or cycloaliphatic epoxide in the conventional ink crosslinked on the substrate by the method of the present invention is less than 0.05 meq / g, preferably less than 0.03 meq / g, and more Preferably it is less than 0.01 meq / g, most preferably less than 0.005 meq / g.

  Preferably, conventional inks crosslinked onto a substrate by the method of the present invention do not contain ethylenically unsaturated groups and cycloaliphatic epoxides.

  Preferably, the liquid ink for use in the present invention comprises a carrier liquid, a resin, a co-resin polymer, and a colorant.

  Preferably, the co-resin comprises an ethylene acrylic acid copolymer, a maleic anhydride polymer with polyethylene grafted onto the polymer, and combinations thereof. The amount of co-resin is 10 to 50 wt%, preferably 10 to 40 wt%, more preferably 10 to 20 wt% of the ink formulation.

  Preferably, the resin is (co) polymer of (meth) acrylic acid; copolymer of (meth) acrylic acid and alkyl (meth) acrylate; copolymer of ethylene and (meth) acrylic acid; copolymer of ethylene and alkyl (meth) acrylate Copolymers of ethylene and (meth) acrylic acid and alkyl (meth) acrylates; copolymers of ethylene and vinyl acetate; copolymers of ethylene and (meth) acrylic acid and vinyl acetate; copolymers of ethylene and alkyl (meth) acrylate and vinyl acetate; Copolymers of ethylene and (meth) acrylic acid, alkyl (meth) acrylate and vinyl acetate; copolymers of (meth) acrylic acid and vinyl acetate; copolymers of alkyl (meth) acrylate and vinyl acetate; (meth) acrylic acid and alkyl (meth) ) Acrylate Copolymers of vinyl acetate; and polyethylene; polystyrene; isotactic polypropylene, polyesters, polyvinyl toluene, polyamides, styrene / butadiene copolymers, epoxy resins, -; including and combinations thereof low molecular weight ethylene polymers such isomers acrylic acid.

  The amount of resin is 5 to 80 wt%, preferably 10 to 60 wt%, more preferably 15 to 40 wt% of the total weight of the ink formulation.

  Preferably, the carrier liquid is (iso) paraffinic hydrocarbon, aliphatic hydrocarbon, isomerized aliphatic hydrocarbon, branched aliphatic hydrocarbon, aromatic hydrocarbon, dearomatized hydrocarbon And hydrocarbons selected from the group consisting of halogenated hydrocarbons, cyclic hydrocarbons, functionalized hydrocarbons, and combinations thereof. Preferably, the carrier is 3,5,7-trimethyldecane.

  The amount of carrier liquid is from 20 to 95% by weight, preferably 40 to 90% by weight, more preferably 60 to 80% by weight of the ink formulation.

  The colorant is an organic and / or inorganic colorant. The colorants can include cyan colorants, magenta colorants, yellow colorants, violet colorants, orange colorants, green colorants, black colorants, and combinations thereof. The amount of colorant is 0.1 to 80% by weight of the ink formulation.

  The ink formulation can further include a charge aid (eg, aluminum tristearate), and a charge directing agent (eg, sulfonic acid or a salt thereof). The charge aid is generally used in an amount of 0.1 to 5% by weight, preferably 0.5 to 4% by weight, more preferably 1 to 3% by weight of the weight of the ink formulation, while the charge directing agent Are generally used in amounts of 0.001 to 1% by weight of the ink formulation.

  Preferably, the flexible packaging substrate is a natural polymeric material (eg cellulose) or synthetic polymeric material (eg polyethylene, polypropylene, polyethylene terephthalate (PET), polyvinyl chloride, polycarbonate, polystyrene, styrene butadiene etc.) And one or more films of a polymer formed from an alkylene monomer of In one example, the substrate comprises or consists of biaxially oriented polypropylene (BOPP).

  In one example, the substrate can comprise cellulosic paper, which can be coated or uncoated cellulosic paper. Coated cellulosic papers include, but are not limited to, cellulosic papers coated with non-cellulosic materials.

  A surface intended to receive digital printing can first be subjected to a physical adaptation treatment (eg plasma treatment, preferably corona plasma treatment, flame treatment, etc.) to modify its surface energy. Another way is to apply a primer on a substrate. The application of this primer can also be preceded by physical surface treatment.

  Primers for use in the present invention can be applied through digital printing. Preferably, the primer comprises a carrier fluid and a resin. Preferably, the carrier is a hydrocarbon as described above. Preferably, the resin is a group consisting of cellulose, dextrin, maltose-hydrate, polyacrylic acid, polyvinyl alcohol, styrene maleic anhydride copolymer, maleimide copolymer, polyacrylamide, sucrose octaacetate, sucrose benzoate, and combinations thereof It is selected from Preferably, the primers for use in the present invention comprise polyacrylamide.

  The term "polyacrylamide" includes all (alkyl) acrylamide ((alk) acrylamides) homopolymers, as well as copolymers and functionalized polyacrylamides. Polyacrylamide can be anionic, cationic or nonionic. Various monomers, preferably ethylenically unsaturated monomers, can be copolymerized with (alkyl) acrylamide monomers to form polyacrylamide.

  The flexible packaging substrate is provided with digital prints, preferably digital prints obtained from liquid electrophotographic printing, and then subjected to electron beam irradiation.

  The flexible packaging substrate of the present invention comprises a primer and one or more ink layers, and the ink layer is digitally printed on at least one side of at least one layer or film constituting the flexible substrate. The total layer thickness of the primer layer and the ink layer is 0.4 to 4 μm, preferably 0.6 to 3.5 μm, more preferably 0.8 to 3 μm, and the layer thickness of the primer is about 0.2 μm .

  In a digital printing press, the substrate is loaded into a starter unwind where it is corona treated to achieve better wettability and ink adhesion. In the next step, a primer is applied to allow covalent bonding between the substrate and the ink. The primer is dried at the drying station and passes through the printing engine. The substrate containing the digital print is subsequently subjected to electron beam impact.

  The electron energy is 10 to 300 keV, preferably 20 to 250 keV, more preferably 30 to 200 keV.

  The received radiation dose of the digitally printed ink is 15 to 100 kGy, preferably 20 to 80 kGy, more preferably 30 to 60 kGy.

  Electron beam irradiation of digital prints is carried out in areas of poor oxygen obtained through the application of a vacuum or through the use of an inert gas blanket such as a nitrogen blanket.

  By "oxygen poor medium" is meant in the present invention an oxygen concentration of less than 300 ppm, preferably less than 250 ppm, more preferably less than 200 ppm, most preferably less than 150 ppm, or even less than 100 ppm.

After electron beam irradiation of the digitally printed substrate, the substrate can be further processed into a laminate, which is subsequently 100 to 250 ° C., preferably 110 to 230 ° C., more preferably Can be heat sealed at a temperature of 120 to 220 ° C. and a pressure of 20 to 120 N / cm ² , preferably 20 to 110 N / cm ² , more preferably 40 to 100 N / cm ² .

  The following illustrative examples are intended only to illustrate the present invention and are not intended to limit or define the scope of the present invention.

Example 1
A 12 μm thick film of polyethylene terephthalate (PET) was treated by Corona (400 W) and subsequently introduced into the HP 20000 Indigo digital printing system. So, it was given a colorless digital primer Digiprime® 050 from Michelman with a layer thickness of about 0.2 μm, and a cyan ink layer was printed thereon with a layer thickness of about 1 μm.

  The digitally printed PET film was then transferred to a vacuum electron beam processor.

  The electron gun has a deflection system. The system was computer controlled and programmed to fire the gun onto a drum which is usually used as a coating drum. The printed film passed through the coating drum and was irradiated by the electron beam gun. The deflection system was programmed to enable electron beam scanning over an area of 200 mm (winding direction) x 400 mm (transverse direction) and was therefore programmed to emit this area. The ink was irradiated for 0.6 seconds by passing the web through this area at a speed of 15 m / min. The electron beam was operated at an accelerating voltage of 35 kV to produce electrons with an energy of 35 keV. The emission current was 0.42 A, resulting in a total radiant power of 15 kW scanning across the area.

  Electron beam irradiated digitally printed PET samples were laminated. Lamination was carried out by using the aromatic adhesive UK2640 / H6800 against an 80 μm thick cast polypropylene film as a sealant layer.

  The PET / PP laminate has two heated jaws at a temperature of 150 ° C., 180 ° C., 200 ° C., 210 ° C. or 220 ° C. and a pressure of 3.5 bar for 0, 6 seconds, outside to outside It was sealed.

  At a dose of 10 kGy and a sealing temperature of 150-220 ° C., the digital prints exhibited drawbacks such as ink removal, ink shrinkage, and gloss change. The above defects disappeared completely with radiation doses of 18 kGy and above.

Example 2
Example 1 was repeated except that the cyan ink was replaced by black ink, magenta ink, orange ink, violet ink, white ink, or yellow ink.

  At an irradiation dose of 10 kGy, digital prints of the respective colors showed the same drawbacks as in Example 1. The above defects disappeared completely with radiation doses of 18 kGy and above.

Example 3 (comparative example)
Example 2 was repeated except that the electron beam irradiation was omitted. Serious printing defects were observed at sealing temperatures above 150 ° C. for all colors.

Example 4 (comparative example)
Each digital print was subjected to electron beam irradiation, but Example 2 was repeated except that the irradiation dose was limited to 15 kGy. Serious printing defects were observed at sealing temperatures above 200 ° C. for all colors.

Example 5
Example 1 was repeated except that the PET film was replaced by 30 μm thick polymer coated paper. The same results as in Example 1 were observed.

Claims (20)

  A flexible packaging substrate comprising one or more digitally printed and electron beam crosslinked ink layers, wherein the concentration of ethylenically unsaturated groups and cycloaliphatic epoxides in said ink layer is less than 0.05 meq / g Preferably less than 0.03 meq / g, more preferably less than 0.01 meq / g, most preferably less than 0.005 meq / g, the crosslinked ink layer being the upper surface of the flexible packaging substrate Flexible packaging base material.   A flexible packaging substrate according to claim 1, characterized in that it does not comprise an additional layer protecting the one or more cross-linked ink layers.   A flexible packaging substrate according to claim 1 or 2, characterized in that it comprises a primer layer sandwiched between the crosslinked ink layer and the substrate.   The total thickness of the primer layer and the ink layer is 0.4 to 4 μm, preferably 0.6 to 3.5 μm, and more preferably 0.8 to 3 μm. Flexible packaging substrate described in   The layer thickness of the primer layer is 0.01 to 0.5 μm, preferably 0.05 to 0.4 μm, most preferably 0.1 to 0.3 μm. Flexible packaging substrate described in A method of forming a printed flexible packaging substrate according to any of the preceding claims, comprising:
a) preparing a flexible packaging substrate;
b) applying at least one digital print by digital printing process of at least one ink composition, wherein said ink composition is less than 0.2 meq / g, preferably less than 0.1 meq / g, more preferably Having a concentration of less than 0.05 meq / g, most preferably less than 0.01 meq / g of ethylenically unsaturated groups, preferably a concentration of (meth) acrylic double bonds, and a concentration of cycloaliphatic epoxides; and c) digital printed matter Subjecting to electron beam irradiation;
A method characterized by comprising.   7. The method according to claim 6, wherein the at least one ink composition is substantially free of a component including a molecular structure having an ethylenic unsaturated double bond which is suspended and / or present at the end. Method.   A method according to claim 6 or 7, characterized in that the flexible packaging substrate is plasma treated, preferably corona plasma treated.   9. A method according to any of claims 6 to 8, characterized in that it comprises the additional step of applying the primer composition before the start of step b).   A method according to any of claims 6 to 9, characterized in that the digital printing process of step b) is liquid electrophotographic printing.   A method according to any of claims 6 to 10, characterized in that the dose of electron beam irradiation in step c) is at least 15 kGy, preferably at least 18 kGy, more preferably at least 20 kGy.   A method according to any of claims 6 to 11, characterized in that the dose of electron beam irradiation in step c) is 20 to 100 kGy, preferably 25 to 80 kGy, more preferably 30 to 60 kGy.   13. The method according to any of claims 6 to 12, characterized in that the electron beam irradiation in step c) is performed at an oxygen concentration of less than 300 ppm, preferably less than 250 ppm, more preferably less than 200 ppm, most preferably less than 150 ppm. the method of.   A method according to any of claims 6 to 13, characterized in that the flexible packaging substrate of step a) comprises polyethylene terephthalate, high density polyethylene, oriented polypropylene, oriented polyamide, polystyrene or paper.   The method according to any one of claims 6 to 14, characterized in that the primer composition comprises one or more polyacrylamides.   A method according to any of claims 6 to 15, characterized in that the ink composition comprises one or more (meth) acrylic (co) polymer resins.   The ink composition comprises 20 to 95% by weight of a hydrocarbon carrier liquid, 5 to 80% by weight of one or more (meth) acrylic (co) polymer resins, and 10 to 50% by weight of one or more carboxyl functional ethylenes. A method according to any of claims 6 to 16, characterized in that it comprises a copolymer containing copolymer and 0.1 to 80% by weight of one or more colorants.   18. A method according to any of claims 6-17, comprising the additional step of laminating a flexible packaging substrate to the sealing layer.   7. Heat sealing the printed flexible packaging substrate or laminate in a heat sealing apparatus at a temperature of 100-250 ° C., preferably 110-230 ° C., more preferably 120-220 ° C. The method according to any of -18.   A flow pack comprising the flexible packaging substrate according to any one of claims 1 to 5.